Systems and methods systems related to electrosurgical wands with screen electrodes

ABSTRACT

An electrosurgical wand for treating tissue at a target site within or on a patient&#39;s body is described, having an elongate shaft with a handle and a distal end portion. The distal end portion has an active electrode, an insulative spacer body and a return electrode; the active electrode supported by the insulative spacer body and spaced away from the return electrode. The active electrode has both lateral and medial edge surfaces. The insulative spacer body has an aspiration cavity fluidly connected with an aspiration lumen, and at least one tapered aperture extending beyond at least one of the electrode medial edge surfaces and directed to the aspiration cavity.

CROSS-REFERENCE TO RELATED APPLICATIONS

None.

FIELD OF THE INVENTION

The present invention relates generally to the field of electrosurgery,and more particularly to apparatus and methods for applying highfrequency voltage to ablate tissue. More particularly, the presentinvention relates to apparatus and methods for securing a substantiallyflat screen-type active electrode to the distal tip of the shaft of anelectrosurgical instrument and methods of fluid aspiration.

BACKGROUND

Electrosurgical systems are used by physicians to perform specificfunctions during surgical procedures. For example, in an ablation modeelectrosurgical systems use high frequency electrical energy to removesoft tissue such as sinus tissue, adipose tissue or other tissue such asmeniscus, or cartilage or synovial tissue in a joint.

Conventional electrosurgical methods are widely used because theygenerally achieve hemostasis and reduce patient bleeding associated withtissue cutting operations while improving the surgeon's visibility ofthe treatment area. Many of the electrosurgical devices used inelectrosurgery include a method of removing fluid, debris and bubblesfrom the field, so as to improve the clinician's visibility around thetarget tissue area. However, in the case of some electrosurgical deviceswhere sufficient fluid is required to achieve certain clinical effects,such as ablation, fluid removal needs to be balanced or targeted inoptimal locations. This may allow sufficient fluid for vapor layer orplasma generation while minimizing debris and bubbles in the field. Manydevices also make use of a screen-type active electrode which istypically cut, or etched, from a sheet of conductive material. Theseelectrosurgical devices and procedures, however, may suffer from anumber of disadvantages. For example, screen-type active electrodestypically require some method of securement to an insulative body andfurthermore to the distal tip of the device itself. Failure toadequately secure the screen electrode to the insulative body may resultin improper device function.

Prior attempts to secure the screen active electrode to the insulativebody have involved mechanical, thermal, and chemical means or variouscombinations thereof. Numerous mechanical forms of securement have beenutilized, while adhesives have been used as a chemical form of joining,and welding the screen may provide a thermal method of joining. Thesemechanical joining methods may also include the use of plastic, ornon-recoverable, deformations of the materials being used forsecurement. However, even in combination with other joining methods, allmethods for fixation provide solutions that typically are challengedover extended periods of use, due to thermal degradation and plasmadegradation. Optimum positioning of the screen electrode fixation withthese methods of degradation therefore must be incorporated.

Accordingly, devices and methods which allow targeted fluid aspirationrelative to ablation surfaces or edges are desired. Additionally,devices for the securement of flat screen active electrodes to theinsulative body of an electrosurgical instrument while maintainingelectrical connections through the insulative body are desired. Inparticular, mechanical methods for providing durable securement of anelectrically connected screen active electrode to the insulative body atthe distal tip of an electrosurgical device, while providing enhancedelectrosurgical operating parameters are desired.

SUMMARY OF THE INVENTION

The present invention provides systems, apparatus and methods foraspirating fluid, debris and gas bubbles from the surgical field and thesurgeon's field of view with minimal interruption to the vapor layer.The present disclosure also provides systems, apparatus and methods formechanically securing a screen type active electrode to the insulativebody at the distal tip of an electrosurgical device. Further the presentdisclosure provides systems and apparatus for creating high currentdensity with internal pointed geometries to decelerate wear on a screenelectrode.

In one aspect of the invention, the present disclosure describes anelectrosurgical wand for treating tissue using a high frequency voltagedelivered to a target site within or on a patient's body. The wandincludes an elongate shaft with a handle end and a distal end portion,the distal end portion having an electrode assembly and an insulativespacer body. The electrode assembly includes both a substantially flatactive screen electrode and a return electrode spaced from the activescreen electrode. The return electrode may be spaced proximally from theactive screen electrode and may be part of the elongate shaft. Theactive electrode is intended to contact tissue and has a relativelylarge tissue contacting surface and a perimeter or edge surface. Theinsulative spacer body contacts tissue in places, and also serves tosupport and electrically insulate the active screen electrode. Anaspiration cavity is disposed within the spacer body with an elongateopening at the tissue contacting surface partially covered by the activescreen electrode, while a portion of the elongate cavity opening extendsbeyond a portion of the screen electrode edge surface. The tissuecontacting surface includes a first aspiration aperture having a firstaperture perimeter, a portion of the first aperture perimeter beingdefined by part of the edge surface of the screen electrode and alsopart of the aspiration cavity.

Another configuration of the electrosurgical device according to thepresent disclosure is an electrosurgical wand for treating tissue at asurgical site with an elongate housing, defining a handle end and atissue contacting surface at a distal end. Part of the tissue contactingsurface includes an active screen electrode which is disposed on aninsulative spacer, this spacer also making up part of the tissuecontacting surface. The active screen electrode includes at least onelateral edge surface, free of any asperities such as surface geometry ortexture that may create an area of high current density such as pointedfeatures or roughened surface, and medial surfaces such as distal andproximal edge surfaces that have at least one asperity such as onepointed geometry feature or area of higher current density. The tissuecontacting surface also includes a first aspiration aperture spaced at adiscrete location away from the at least one lateral edge surface so asto not disrupt any plasma or vapor layer proximate the lateral edgesurface. This aperture is in fluid communication with an aspirationlumen disposed within the wand and may remove any debris or gas bubblesfrom the surgical site. This first aperture has a perimeter thatincludes a portion of an insulating spacer cavity and a portion ofeither the electrode distal edge surface or the electrode proximal edgesurface.

In another aspect of the disclosure, a method of treating a targettissue using an electrosurgical wand is described, the method includingplacing a distal end portion of the wand near a target tissue, thedistal end portion including a substantially flat active screenelectrode being supported by an insulative spacer. A high frequencyvoltage may then be applied between the active electrode and a returnelectrode that is spaced away from the active electrode, the highfrequency voltage is sufficient to generate a vapor layer near a tissuecontacting surface of the active electrode. The distal end portion maythen be oriented so that a lateral edge surface of the active electrodeis near the target tissue so as to use this edge surface, primarily totreat the target tissue. Tissue fragments and gas bubbles may then beaspirated away through at least one aspiration aperture that is locatedin a discrete area that is spaced away from the lateral edge surface.This is so as to not disrupt the vapor layer proximate the activeelectrode lateral edge surface, to therefore maintain a uniform vaporlayer near the lateral edge surface so as to create a more consistentelectrosurgical tissue effect. The at least one aspiration aperture hasa portion of its perimeter made up by the active screen electrode and aportion by a spacer aspiration cavity.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of exemplary embodiments, reference will nowbe made to the accompanying drawings in which:

FIG. 1 shows an electrosurgical system in accordance with at least someembodiments;

FIG. 2 shows an electrosurgical wand in accordance with at least someembodiments;

FIG. 3a shows a perspective view of a wand distal end in accordance withat least some embodiments;

FIG. 3b illustrates a view of a wand contact surface in accordance withat least some embodiments;

FIG. 3c shows a wand distal end cross-sectional view in accordance withat least some embodiments;

FIG. 4 shows a perspective view of an insulating spacer of a wand inaccordance with at least some embodiments;

FIG. 5 shows an elevation view of the distal end of a wand treatingtissue in accordance with at least some embodiments;

FIG. 6 shows a method of treating tissue in accordance with at leastsome embodiments; and

FIG. 7 shows a method of treating tissue in accordance with at leastsome embodiments.

NOTATION AND NOMENCLATURE

Certain terms are used throughout the following description and claimsto refer to particular system components. As one skilled in the art willappreciate, companies that design and manufacture electrosurgicalsystems may refer to a component by different names. This document doesnot intend to distinguish between components that differ in name but notfunction.

In the following discussion and in the claims, the terms “including” and“comprising” are used in an open-ended fashion, and thus should beinterpreted to mean “including, but not limited to . . . . ” Also, theterm “couple” or “couples” is intended to mean either an indirect ordirect connection. Thus, if a first device couples to a second device,that connection may be through a direct connection or through anindirect connection via other devices and connections.

Reference to a singular item includes the possibility that there areplural of the same items present. More specifically, as used herein andin the appended claims, the singular forms “a,” “an,” “said” and “the”include plural references unless the context clearly dictates otherwise.It is further noted that the claims may be drafted to exclude anyoptional element. As such, this statement serves as antecedent basis foruse of such exclusive terminology as “solely,” “only” and the like inconnection with the recitation of claim elements, or use of a “negative”limitation. Lastly, it is to be appreciated that unless definedotherwise, all technical and scientific terms used herein have the samemeaning as commonly understood by one of ordinary skill in the art towhich this invention belongs.

“Active electrode” shall mean an electrode of an electrosurgical wandwhich produces an electrically-induced tissue-altering effect whenbrought into contact with, or close proximity to, a tissue targeted fortreatment, and/or an electrode having a voltage induced thereon by avoltage generator.

“Return electrode” shall mean an electrode of an electrosurgical wandwhich serves to provide a current flow path for electrons with respectto an active electrode, and/or an electrode of an electrosurgical wandwhich does not itself produce an electrically-induced tissue-alteringeffect on tissue targeted for treatment.

Where a range of values is provided, it is understood that everyintervening value, between the upper and lower limit of that range andany other stated or intervening value in that stated range isencompassed within the invention. Also, it is contemplated that anyoptional feature of the inventive variations described may be set forthand claimed independently, or in combination with any one or more of thefeatures described herein.

All existing subject matter mentioned herein (e.g., publications,patents, patent applications and hardware) is incorporated by referenceherein in its entirety except insofar as the subject matter may conflictwith that of the present invention (in which case what is present hereinshall prevail). The referenced items are provided solely for theirdisclosure prior to the filing date of the present application. Nothingherein is to be construed as an admission that the present invention isnot entitled to antedate such material by virtue of prior invention.

DETAILED DESCRIPTION

The present invention provides systems and methods for selectivelyapplying electrical energy to a target location within or on a patient'sbody. The present invention is particularly useful in procedures wherethe tissue site is flooded or submerged with an electrically conductingfluid, such as arthroscopic surgery of the knee, shoulder, ankle, hip,elbow, hand or foot. In other procedures, the present invention may beuseful for collagen shrinkage, ablation and/or hemostasis in proceduresfor treating target tissue alone or in combination with the volumetricremoval of tissue. More specifically, the embodiments described hereinprovide for electrosurgical devices characterized by a substantiallyflat and relatively thin screen active electrode disposed at the distaltip of the device. Additionally, the present embodiments includeapparatus and methods for the targeted aspiration of fluid and debrisaway from the surgical field as well as methods of mechanical securementof the screen electrode and wear resistant design features to the screenelectrode. These embodiments may extend the operating period of theelectrosurgical device by providing a more wear resistant electrode toplasma and a more robust electrode securement method of attachment.These embodiments may also improve the surgeon's visibility of thesurgical field while minimizing any disruption to a vapor layer aroundthe screen electrode and hence any disruption to the intended tissueeffect.

Before the present invention is described in detail, it is to beunderstood that this invention is not limited to particular variationsset forth herein as various changes or modifications may be made to theinvention described and equivalents may be substituted without departingfrom the spirit and scope of the invention. As will be apparent to thoseof skill in the art upon reading this disclosure, each of the individualembodiments described and illustrated herein has discrete components andfeatures which may be readily separated from or combined with thefeatures of any of the other several embodiments without departing fromthe scope or spirit of the present invention. In addition, manymodifications may be made to adapt a particular situation, material,composition of matter, process, process act(s) or step(s) to theobjective(s), spirit or scope of the present invention. All suchmodifications are intended to be within the scope of the claims madeherein.

Methods recited herein may be carried out in any order of the recitedevents which is logically possible, as well as the recited order ofevents. Furthermore, where a range of values is provided, it isunderstood that every intervening value, between the upper and lowerlimit of that range and any other stated or intervening value in thatstated range is encompassed within the invention. Also, it iscontemplated that any optional feature of the inventive variationsdescribed may be set forth and claimed independently, or in combinationwith any one or more of the features described herein.

All existing subject matter mentioned herein (e.g., publications,patents, patent applications and hardware) is incorporated by referenceherein in its entirety except insofar as the subject matter may conflictwith that of the present invention (in which case what is present hereinshall prevail). The referenced items are provided solely for theirdisclosure prior to the filing date of the present application. Nothingherein is to be construed as an admission that the present invention isnot entitled to antedate such material by virtue of prior invention.

Reference to a singular item, includes the possibility that there areplural of the same items present. More specifically, as used herein andin the appended claims, the singular forms “a,” “an,” “said” and “the”include plural referents unless the context clearly dictates otherwise.It is further noted that the claims may be drafted to exclude anyoptional element. As such, this statement is intended to serve asantecedent basis for use of such exclusive terminology as “solely,”“only” and the like in connection with the recitation of claim elements,or use of a “negative” limitation. Last, it is to be appreciated thatunless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs.

FIG. 1 illustrates an electrosurgical system 100 in accordance with atleast some embodiments. In particular, the electrosurgical system 100comprises an electrosurgical wand 102 (hereinafter “wand 102”) coupledto an electrosurgical controller 104 (hereinafter “controller 104”). Thewand 102 comprises an elongate housing or elongate shaft 106 thatdefines distal end 108. The elongate shaft 106 further defines a handleor proximal end 110, where a physician grips the wand 102 duringsurgical procedures. The wand 102 further comprises a flexiblemulti-conductor cable 112 housing one or more electrical leads (notspecifically shown in FIG. 1), and the flexible multi-conductor cable112 terminates in a wand connector 114. As shown in FIG. 1, the wand 102couples to the controller 104, such as by a controller connector 120 onan outer surface of the enclosure 122 (in the illustrative case of FIG.1, the front surface).

Though not visible in the view of FIG. 1, in some embodiments the wand102 has one or more internal fluid conduits coupled to externallyaccessible tubular members. As illustrated, the wand 102 has a flexibletubular member 116, used to provide aspiration at the distal end portion108 of the wand. In accordance with various embodiments, the tubularmember 116 couples to a peristaltic pump 118, the pump beingillustratively shown as an integral component with the controller 104.In other embodiments, an enclosure for the peristaltic pump 118 may beseparate from the enclosure 122 for the controller 104 (as shown bydashed lines in the figure), but in any event the peristaltic pump isoperatively coupled to the controller 104. In the context of the variousembodiments, the peristaltic pump 118 creates a volume-controlledaspiration from a surgical field at the distal end portion 108 of thewand 102.

Still referring to FIG. 1, a display device or interface device 130 isvisible through the enclosure 122 of the controller 104, and in someembodiments a user may select operational modes of the controller 104 byway of the interface device 130 and related buttons 132. In someembodiments the electrosurgical system 100 also comprises a foot pedalassembly 134. The foot pedal assembly 134 may comprise one or more pedaldevices 136 and 138, a flexible multi-conductor cable 140 and a pedalconnector 142. While only two pedal devices 136 and 138 are shown, oneor more pedal devices may be implemented. The enclosure 122 of thecontroller 104 may comprise a corresponding connector 144 that couplesto the pedal connector 142. A physician may use the foot pedal assembly134 to control various aspects of the controller 104, such as theoperational mode. For example, pedal device 136 may be used for on-offcontrol of the application of radio frequency (RF) energy to the wand102. Further, pedal device 138 may be used to control and/or set themode of ablation of the electrosurgical system. In certain embodiments,control of the various operational or performance aspects of controller104 may be activated by selectively depressing finger buttons located onhandle 110 of wand 102 (the finger buttons not specifically shown so asnot to unduly complicate the figure).

The electrosurgical system 100 of the various embodiments may have avariety of operational modes. One such mode employs Coblation®technology. In particular, the assignee of the present disclosure is theowner of Coblation® technology. Coblation® technology involves theapplication of RF energy between one or more active electrodes and oneor more return electrodes of the wand 102 to develop high electric fieldintensities in the vicinity of the target tissue. The electric fieldintensities may be sufficient to vaporize an electrically conductivefluid over at least a portion of the one or more active electrodes inthe region between the one or more active electrodes and the targettissue. The electrically conductive fluid may be inherently present inthe body, such as blood, or in some cases extracelluar or intracellularfluid. In other embodiments, the electrically conductive fluid may be aliquid or gas, such as isotonic saline. In some embodiments theelectrically conductive fluid is delivered in the vicinity of the activeelectrodes and/or to the target site by the wand 102.

When the electrically conductive fluid is heated to the point that theatoms of the fluid vaporize faster than the atoms condense, a vapor orgas is formed. When sufficient energy is applied to the vapor or gas,the atoms collide with each other causing a release of electrons in theprocess, and an ionized gas, ionized vapor layer, or plasma is formed(the so-called “fourth state of matter”). Stated otherwise, plasmas maybe formed by heating a gas and ionizing the gas by driving an electriccurrent through the gas, or by directing electromagnetic waves into thegas. The methods of plasma formation give energy to free electrons inthe plasma directly, electron-atom collisions liberate more electrons,and the process cascades until the desired degree of ionization isachieved. A more complete description of plasma can be found in PlasmaPhysics, by R. J. Goldston and P. H. Rutherford of the Plasma PhysicsLaboratory of Princeton University (1995), the complete disclosure ofwhich is incorporated herein by reference.

As the density of the plasma becomes sufficiently low (i.e., less thanapproximately 1020 atoms/cm³ for aqueous solutions), the electron meanfree path increases such that subsequently injected electrons causeimpact ionization within the plasma. When the ionic particles in theplasma layer have sufficient energy (e.g., 3.5 electron-Volt (eV) to 5eV), collisions of the ionic particles with molecules that make up thetarget tissue break molecular bonds of the target tissue, dissociatingmolecules into free radicals which then combine into gaseous or liquidspecies. Often, the electrons in the plasma carry the electrical currentor absorb the electromagnetic waves and, therefore, are hotter than theionic particles. Thus, the electrons, which are carried away from thetarget tissue toward the active or return electrodes, carry most of theplasma's heat, enabling the ionic particles to break apart the targettissue molecules in a substantially non-thermal manner.

By means of the molecular dissociation (as opposed to thermalevaporation or carbonization), the target tissue is volumetricallyremoved through molecular dissociation of larger organic molecules intosmaller molecules and/or atoms, such as hydrogen, oxygen, oxides ofcarbon, hydrocarbons and nitrogen compounds. The molecular dissociationcompletely removes the tissue structure, as opposed to dehydrating thetissue material by the removal of liquid within the cells of the tissueand extracellular fluids, as occurs in related art electrosurgicaldesiccation and vaporization. A more detailed description of themolecular dissociation can be found in commonly assigned U.S. Pat. No.5,697,882, the complete disclosure of which is incorporated herein byreference.

In addition to the Coblation® mode, the electrosurgical system 100 ofFIG. 1 is also useful for sealing larger arterial vessels (e.g., on theorder of about 1 millimeter (mm) in diameter), when used in what isknown as a coagulation mode. Thus, the system of FIG. 1 may have anablation mode where RF energy at a first voltage is applied to one ormore active electrodes sufficient to effect molecular dissociation ordisintegration of the tissue, and the system of FIG. 1 may also have acoagulation mode where RF energy at a second, lower voltage is appliedto one or more active electrodes (either the same or differentelectrode(s) as the ablation mode) sufficient to heat, shrink, seal,fuse, and/or achieve homeostasis of severed vessels within the tissue.

The energy density produced by electrosurgical system 100 at the distalend 108 of the wand 102 may be varied by adjusting a variety of factors,such as: the number of active electrodes; electrode size and spacing;electrode surface area; asperities and/or sharp edges on the electrodesurfaces; electrode materials; applied voltage; current limiting of oneor more electrodes (e.g., by placing an inductor in series with anelectrode); electrical conductivity of the fluid in contact with theelectrodes; density of the conductive fluid; and other factors.Accordingly, these factors can be manipulated to control the energylevel of the excited electrons.

FIG. 2 illustrates a view of the wand 102 in accordance with examplesystems. In the illustrated embodiment the elongate shaft 106 is made ofa metallic material (e.g., Grade TP304 stainless steel hypodermictubing), and in some cases the elongate shaft 106 also defines a returnelectrode for the system. The wand 102 such as the embodiment shown inFIG. 2 may be designed for surgical procedures involving the knee orhip. The illustrated embodiment's elongate shaft 106 has a circularcross-sectional shape with a bend towards the distal end 108, orientingdistal end 108 approximately 40° relative to the elongate axis of theproximal portion of shaft 106. Additionally distal end surface isoriented at an angle to the elongate axis of the shaft 106, cut atapproximately a 30° angle relative to the distal end of the shaft 106,to define an oval shaped distal end surface 250 (better illustrated inFIGS. 3a and 3b ). This provides for a lower wand distal end profile inorder to accommodate space restrictions and posterior anatomy access.For embodiments where the cross-sectional shape of the elongate shaft106 is circular, the outside diameter may be on the order of about 3millimeters (mm), but larger and smaller dimensions may be used.

In embodiments where the elongate shaft is metallic, the distal endportion 108, as illustrated in FIG. 3a , may further comprise anelectrically insulative spacer 200 coupled to the elongate shaft 106. Insome cases spacer 200 is ceramic, but other non-conductive materialsresistant to degradation when exposed to plasma may be equivalently used(e.g., glass). Spacer 200 may couple to the elongate shaft 106 in anysuitable manner, such as telescoping within an inside diameter of theelongate shaft 106, by telescoping over the elongate shaft 106, and/orby use of adhesive. As shown in FIG. 3c , spacer 200 has a telescopingportion 266 operable to be placed within the internal diameter of theelongate housing 106 and in some cases the spacer may be at leastpartially held in place by an adhesive. Spacer 200 supports at least oneactive screen electrode 202 constructed of metallic or electricallyconductive material. Spacer 200 thus electrically insulates activeelectrode 202 from the elongate shaft 106, as the elongate shaft 106 mayact as the return electrode 203. In some embodiments, only a portion ofelongate shaft 106 is exposed to act as return electrode 203, with theremaining portion of shaft 106 covered with an insulating material.

The illustrative active screen electrode 202 may comprise a conductivematerial, such as tungsten, titanium, molybdenum, stainless steel,aluminum, gold, copper or the like. Screen electrode 202 may have adiameter in the range of about 0.5 to 8 mm, preferably about 1 to 4 mm,and a thickness of about 0.05 to about 2.5 mm, preferably about 0.1 to0.5 mm. Screen electrode 202 may have a variety of different shapes,such as the shape shown in FIGS. 3a and 3b , including at least onelateral edge surface 205 having a continuous edge surface free of anyasperities such as pointed geometries. Lateral edge surface 205 islaterally spaced away from all aspiration apertures, such as aperture206, 254 and 252 that are disposed more medially on the wand 102, sothat a vapor layer may form adjacent a lateral edge surface 205 andremain relatively undisturbed during any aspiration. Screen electrode202 may also include medial edge surfaces, such as a distal edge surface210 and proximal edge surface 212, at least one of which may include atleast one asperity such as an internal pointed geometry feature or cusp214 a, b, or some form of pointed or edged surface geometry. A surfaceasperity such as an internal pointed geometry feature creates a point ofhigher current density that leads to a preferential point of vapor layerinitiation and potentially plasma generation on the active electrode202. Without cusps 214 a, b, vapor layer initiation may require highervoltages. Illustrated best in FIGS. 3a and 3b , active electrode 202 hasfour inverted cusps 214 a of varying sizes disposed on the distal edgesurface 210 and another four inverted cusps 214 bof varying sizes on theproximal edge surface 212. These are disposed at a specific, distinctlocation advantageous for enhanced vapor layer formation and potentiallysubsequent plasma formation, but spaced medially away from lateral edgesurfaces 205.

In particular, inverted cusps 214 a, b may be defined by curved portions209 that tangentially intersect at a point 230. Inverted cusps 214 a, bhave a consistent or uniform shape throughout the thickness of activeelectrode 202, so that the point of intersection 230 creates anelongated surface or line, with minimal transition or radius betweenadjacent curved portions 209, through the thickness of screen electrode202. Inverted cusps 214 a, b create a point of vapor layer initiation toimprove vapor layer formation and potentially plasma formation,proximate the point of intersection 230 for smooth tissue cutting.Unlike other plasma and vapor layer initiating asperities known in theart, such as externally protruding points or alternatively edges orcorners of electrodes, the inverted cusp provides a vapor layerinitiation point that minimizes tissue snagging during wand andelectrode motion across tissue surfaces during tissue treatment.Additionally, the use of inverted cusps 214 a, bas formed byintersection 230 appear to provide the unexpected benefit of moreconsistent and predicable patterns of active electrode 202 material wearand erosion. Illustrated best in FIG. 3b , inverted cusps 214 a and 214b have a variety of depths and curves so that point 230 may be spaced tovarying degrees from the electrode distal edge surface 210 or theproximal edge surface 212. It has been found during typical wandoperation that the distal edge surface 210 tends to preferentially eroderelative to the proximal edge surface 212. One reason for this is as aresult of a typical wand orientation during tissue treatment, whichleads to a preferred vapor layer initiation at the more distal portionof the electrode 202. The inventors have also found that in thisparticular orientation the flow rate of fluid drawn into the aspirationaperture is higher at the distal portion of electrode 202 and as drawninto aperture 252. Erosion rates of the material of electrode 202 havebeen found to be directly related to the proximity of the cusps to areasof higher fluid aspiration. Therefore, adjacent to aspiration apertureswith relatively higher rates of fluid flow (e.g., adjacent aperture 252in the presently describe configuration), distal cusps 214 a have afirst or reduced depth (d) relative to cusps 214 b with a second depthD, or larger depth D to accommodate these differing erosion rates. Byadjusting the depth of the cusps in areas with proximity to preferredvapor layer initiation characteristics and higher fluid aspirationrates, the inventors have found that the useful life of electrode 202may be extended.

Screen electrode 202 may comprise aspiration aperture 206 having sizesand configurations that may vary depending on the particularapplication. Electrode aspiration aperture 206 will typically be largeenough to allow ablated tissue fragments to pass through into anaspiration cavity and suction lumen (described in later figures) withininsulative spacer 200 and flexible tubular member 116. Electrodeaspiration aperture 206 is disposed in approximately the centre of theactive electrode 202 and is spaced away from at least one lateral edgesurface 205. Shown here, aspiration aperture 206 is spaced approximatelyequidistant between the two lateral edge surfaces 205. Screen electrode202 may also have at least one securing wire aperture 216 sized toreceive a securing wire or ribbon 220 operable to secure active screenelectrode 202 to spacer 200. Wire or ribbon 220 may comprise aconductive material, such as platinum iridium and is operable to performmultiple functions. Firstly securement wire 220 is electricallyconnected with cable 112, disposed within elongate shaft 106 as well asactive screen electrode 202, so as to be part of the electrical conduitthrough which the RF controller 104 delivers energy to the active screenelectrode 202. Securement ribbon 220 may protrude through the at leastone securing wire aperture 216 (as shown in FIG. 3b ) and be processedso as to provide both a permanent electrical contact and mechanicalsecurement with the active electrode 202 (shown in welded form 221 inFIG. 3a ). This process may include laser spot welding. Securement wire220 is preferably constructed from a material having a lower meltingtemperature than the active screen electrode material so as to meltreadily during laser spot welding without affecting the grain structureof the active electrode 202. Structural changes to the active electrode202 may reduce resistance to plasma degradation during the use.Securement wire 220 must also comprise a material with substantialresistance to plasma degradation itself, so that the laser spot weld,and hence mechanical securement and electrical continuity, minimallydegrades with use.

Screen electrode 202 has an exposed tissue contacting surface 204, aswell as an inner surface (not shown here) that abuts the spacer topsurface 250. A portion of spacer top surface 250 also forms part of thetissue contacting surface. Screen electrode 202 abuts spacer top surface250 with minimal gaps, deterring fluid ingress and energy misdirection.In some embodiments, such as that shown in FIG. 3a , active electrode202 defines an exposed lateral edge surface 205, free of any asperitiesor internal pointed geometry 214 a, b to allow a side ablative effectfor application on certain more sensitive tissue types such ascartilage. Use of the lateral edge surface 205 also allows for maximumvisibility of the electrode surface 204 and the associated tissueeffect. As shown in FIG. 3c , a cross section A-A of FIG. 3b , activeelectrode aperture 206 is fluidly coupled to the flexible tubular member116 (shown in FIG. 3c ) via a spacer aspiration cavity 256.

As illustrated best in FIGS. 3b, 3c and FIG. 4, spacer cavity 256defines an elongate shaped opening at spacer top surface 250. Spacercavity 256 fluidly communicates with electrode aperture 206 and extendsin a proximal and distal direction beyond the proximal edge surface 212and distal edge surface 210 of active electrode 202, so as to define adistal aperture 252 and proximal aperture 254. Spacer cavity 256 tapersfrom an elongate opening at the top surface 250 to an approximatecircular cross section 255 within spacer 200 which gives cavity 256 anelongated funnel-like shape. Cavity taper may have an angle in the rangeof about 140-170°, and preferably about a 157° angle relative to thecontact surface 204 as shown in FIG. 3c . This angle defines a maximumgap X between the active electrode inner surface 218 and beginning ofcircular cross section 255 of aspiration conduit, so as to minimizeclogging of the aspiration tubing and conduits due to larger debrissizes. Gap X may be in the range of about 0.1 to 1 mm, preferably about0.3-0.6 mm. Debris or tissue fragments larger than gap X in dimensionwill become trapped within gap X and continue to be fragmented by theablative effect proximate active electrode inner surface 218 until thedebris or tissue fragment is reduced in size, free to be aspiratedthrough cross section 255 while being less likely to clog any downstreamaspiration conduits or lumens, such as lumen 116.

Spacer cavity 256, via apertures 252, 254 and in cooperation with thescreen electrode distal and proximal edge surfaces 210 and 212respectively, define a multitude of aspiration apertures adjacent to orat the electrode contact surface 204, all of which are fluidly connectedwithin cavity 256 of spacer 200. Distal aperture 252 has a continuousperimeter defined partially by the electrode distal edge surface 210 andpartially by the distal portion of the spacer cavity 256. As shown inFIG. 3b , the perimeter also includes at least one internal cusp 214 a.Proximal aperture 254 has a perimeter defined partially by the electrodeproximal edge surface 212, including at least one cusp 214 b andpartially by a proximal portion of the cavity 256. Proximal aperture 254extends a first distance “E” beyond active electrode proximal edge 212,while distal aperture 252 extends a second distance “e” beyond activeelectrode distal edge 210. In order to have a more balanced flow betweenthe distal aperture 252 and proximal aperture 254, it has been foundthat extension “E” should be larger than extension “e”. This is due todiffering aspiration rates between the two apertures (252 and 254)predominantly as a result of the difference in transitions angles, 260and 262. Looking at FIG. 3c , it can be seen that transition angle 260defines a shallower angle relative to transition angle 262, and resultsin a preferential aspiration of debris through the distal aperture 252.Increased aspiration may lead to preferential electrode erosion adjacentthe area of increased aspriation, so proximal aperture 254 is thereforerelatively larger than distal aperture 252 in order to better balanceaspiration flow across the tissue contact surface 204 and to mitigatepotential erosion to any particular portion of the active electrode 202around each aperture.

Spacer apertures 252 and 254 and electrode aperture 206 provide conduitsfor fluid and gas bubbles to be aspirated away from the area surroundingactive electrode 202. During arthroscopic surgical procedures the visualfield near the surgical site (i.e., near the active electrode) may beobscured by gas bubbles. That is, the process of ablation via tissuecontact with the vapor layer described above creates gas bubbles, and inmany situations the gas bubbles are quickly aspirated away so as notadversely affect the visual field. However, excessive aspiration tooclose to a portion of the active electrode 202 that is treating thetarget tissue may interrupt the vapor layer and hence the uniformity ofablative tissue effect. Apertures 206, 252 and 254 are therefore spacedaway, in discrete locations, from the lateral side edge surface 205.Apertures 206, 252 and 254 are disposed between the lateral side edgesurface 205 and the primary surgical field viewing portal so as toeffectively remove bubbles created predominantly at lateral edge surface205 which then naturally elevate towards apertures 206, 252 and 254.This is thought to improve surgeon visibility of the surgical fieldwhile minimally impacting the vapor layer near the lateral edge surface205.

A detailed perspective view of spacer is shown in FIG. 4, in accordancewith some embodiments, to better describe spacer cavity 256 andsecurement wire conduits 258. Spacer cavity 256 may be shaped in anelongate funnel form or plenum within spacer that tapers to a morecircular cross section 255 (see in FIG. 3c ) at a more proximal locationof spacer 200, so as to interface with a fluid tube 116 (shown in FIG.3c ) disposed within elongate shaft. Securement wire conduits 258 may beuniform in cross section and extend axially through the entire thicknessof spacer 200 to allow passage for securement wires 220 through spacer200. Spacer 200, being made from an electrical insulating material, mayelectrically isolate securement wires 220 (shown in FIG. 3b ) from eachother as well as from return electrode 203. In alternative embodiments,securement wires 220 may have an electrically insulative coating.Securement wires 220 extend proximally through shaft 106 and mayelectrically couple with multi-conductor cable 112 within handle 110(not shown here).

FIG. 5 representatively illustrates in greater detail a typicaltreatment of a target tissue 300 by use of an embodiment ofelectrosurgical wand 102 according to the present disclosure. Initially,surgeon may place a spacer lateral side 240 on the tissue and roll wanddistal end portion 108 toward spacer lateral edge bevel 241 whileapplying energy, until a tissue effect is observed. This will occur onceelectrode lateral edge surface 205 is sufficiently close to targettissue 300, or in contact. As shown, the high frequency voltage issufficient to convert the electrically conductive fluid 310 between thetarget tissue 300 and active electrode 202 into a vapor layer 312 orplasma.

During the process, gases 320 and debris will be aspirated throughapertures 206, 252 or 254 to a vacuum source (not shown). In addition,excess electrically conductive fluid, and other fluids (e.g., blood)will be aspirated from the target site 300 to facilitate the surgeon'sview. Gas bubbles 320 may naturally rise from the vapor or plasma layer312, upwards or in a medial direction towards apertures 206, 252 or 254and be removed so as to improve surgeon's target tissue visualization.

FIG. 6 shows a method in accordance with at least some embodiments. Inparticular, the method starts (block 600) and proceeds to: placing adistal end portion of the wand proximate a target tissue, the distal endportion comprising a substantially flat active screen electrode and aninsulative spacer, the screen electrode supported by the spacer (block602); applying a high frequency voltage between the active electrode anda return electrode spaced away from the active electrode, the highfrequency voltage sufficient to generate a vapor layer or plasmaproximate a tissue contacting surface of the active electrode (block604); orienting the distal end portion so that a lateral edge surface ofthe active electrode is proximate a target tissue and treating thetarget tissue (block 606); and aspirating tissue fragments and gasbubbles through at least one aspiration aperture disposed in a discretearea spaced away from the lateral edge surface so as to not disrupt thevapor layer or plasma proximate the active electrode lateral edgesurface, wherein the at least one aspiration aperture is defined by aportion of the active screen electrode and a portion of a spaceraspiration cavity (block 608). The method may also include at leastthree aspiration apertures and wherein the step of aspirating furthercomprises aspirating the tissue fragments and gas bubbles approximatelyequally through the at least three aspiration apertures, wherein the atleast three apertures are coplanar on a plane spaced away from thelateral edge surface and the at least three apertures are approximatelyevenly spaced and of differing sizes so as to uniformly aspirate along alength of the lateral edge surface. The method may also includegenerating a vapor layer or plasma proximate a geometric feature capableof creating a point of high current density on the active electrode,wherein the geometric feature may comprise an internal cusp. Thereafter,the method ends (block 610).

FIG. 7 shows a method in accordance with at least some embodiments. Inparticular, the method starts (block 700) and proceeds to: creating avapor layer proximate to a first edge surface of an active electrodedisposed at the distal end of an electrosurgical wand so as to treat atarget tissue, wherein the first edge surface is free from any points ofhigh current density (block 702); drawing fluid and tissue fragmentsthrough a first aperture defined by the active electrode only and spacedaway from the vapor layer proximate the first edge surface (block 704),drawing fluid and tissue fragments through a second aperture thatextends beyond an active electrode edge surface, the second apertureperimeter defined in part by a second edge surface of the activeelectrode and in part by a portion of an insulating spacer cavity, thesecond edge surface having at least one internal or external pointedgeometry or surface asperity, and wherein the second aperture is alsospaced away from the vapor layer proximate the first edge surface of theactive electrode and also spaced away from the first aperture (block706). The method may further comprise drawing fluid and tissue fragmentsthrough a third aperture, the third aperture defined in part by a thirdedge surface of the active electrode and in part by a portion of theinsulating spacer cavity and wherein the first, second and thirdaperture are all fluid coupled. Thereafter, the method ends (block 708).

While preferred embodiments of this disclosure have been shown anddescribed, modifications thereof can be made by one skilled in the artwithout departing from the scope or teaching herein. The embodimentsdescribed herein are exemplary only and are not limiting. Because manyvarying and different embodiments may be made within the scope of thepresent inventive concept, including equivalent structures, materials,or methods hereafter though of, and because many modifications may bemade in the embodiments herein detailed in accordance with thedescriptive requirements of the law, it is to be understood that thedetails herein are to be interpreted as illustrative and not in alimiting sense.

What is claimed is:
 1. An electrosurgical wand for treating tissue at atarget site within or on a patient's body comprising: an elongate shafthaving a handle end and a distal end portion, the distal end portioncomprising an active electrode, an insulative spacer body and a returnelectrode, wherein the active electrode is supported on the insulativespacer body and is spaced away from the return electrode; wherein theactive electrode defines a peripheral edge surface; wherein theinsulative spacer body defines an aspiration cavity fluidly connectedwith an aspiration lumen and terminating with a cavity aperture having aperimeter, wherein the active electrode partially cover the cavityaperture so as to define at least one aspiration aperture having anaspiration aperture perimeter that is defined by the cavity apertureperimeter and the active electrode peripheral edge surface.
 2. Theelectrosurgical wand of claim 1 wherein the peripheral edge surfacedefines at least one active electrode lateral edge surface portion freeof any asperities and spaced away from the cavity aperture.
 3. Theelectrosurgical wand of claim 1 wherein the active electrode furthercomprises an electrode aperture in fluid communication with theaspiration cavity and spaced away from the active electrode peripheraledge surface.
 4. The electrosurgical wand of claim 1, wherein the atleast one aspiration aperture comprises at least two aspirationapertures each having a perimeter defined by the active electrodeperipheral edge surface and the cavity aperture perimeter.
 5. Theelectrosurgical wand of claim 4 wherein the at least two aspirationapertures comprise a first and second aspiration aperture, the firstaspiration aperture smaller than the second aspiration aperture.
 6. Theelectrosurgical wand of claim 5 wherein the first aspiration aperturehas a perimeter defined by a portion of the peripheral edge surfacehaving at least one internal cusp with a first depth and the secondaspiration aperture has a perimeter defined by a portion of theperipheral edge surface having at least one internal cusp with a seconddepth and wherein the first cusp depth is significantly smaller than thesecond cusp depth and wherein the cusps are configured to create aninternal point of higher current density and preferential vapor layerformation.
 7. The electrosurgical wand of claim 1 wherein the peripheraledge surface further comprises at least one internal cusp, configured tocreate a point of high current density for preferential vapor layerformation.
 8. The electrosurgical wand of claim 7 wherein the at leastone internal cusp is defined by an intersection between two adjacentcurved portions, the intersection characterized by an internal pointedfeature.
 9. The electrosurgical wand of claim 1 further comprising atleast one securing wire of conductive material, electrically coupled toand mechanically secured to a tissue contacting surface of the activeelectrode and wherein the at least one securing wire is disposed along apath defined by at least one active electrode wire aperture, at leastone spacer body wire conduit and the elongate shaft and wherein the atleast one securing wire is in electrical communication with a highfrequency energy source.
 10. The electrosurgical wand of claim 1 whereinthe aspiration cavity is characterized by an elongate funnel shape sothat the cavity aperture defines a first dimension and second dimensionthat is less than the first dimension.
 11. The electrosurgical wand ofclaim 10 wherein the aspiration cavity tapers so as to define a maximumgap within the aspiration cavity, the gap configured so as to trap anylarger tissue fragments within the aspiration cavity so that the tissuefragments are further ablated by a portion of the active electrodebefore allowing the fragments to pass into the aspiration lumen.
 12. Theelectrosurgical wand of claim 1 wherein the aspiration cavity has atapered surface.
 13. An electrosurgical wand for treating tissue at atarget site within or on a patient's body comprising: an elongate shafthaving a handle end and a distal end portion, the distal end portioncomprising an active electrode, an insulative spacer body and a returnelectrode, wherein the active electrode is disposed on a first surfaceof the insulative spacer body and is spaced away from the returnelectrode; wherein the active electrode comprises an outer edge surfacedefining first and second lateral and medial edge surface portions;wherein the insulative spacer body defines an aspiration cavity fluidlyconnected with an aspiration lumen and at least one aspiration aperture,the at least one aspiration aperture having a perimeter at leastpartially defined by at least one of the medial edge surface portions.14. The electrosurgical wand of claim 13, the at least one aspirationaperture comprising a first and second aspiration aperture, the firstaspiration aperture having a perimeter at least partially defined by thefirst medial edge portion and the second aspiration aperture having aperimeter at least partially defined by the second medial edge surfaceportion.
 15. The electrosurgical wand of claim 14 wherein the first andsecond medial edge surface portions of the active electrode each furthercomprise at least one internal cusp, wherein at least one internal cuspis configured so as to create a preferential point of vapor layerformation, and wherein the at least one internal cusp is disposed alongat least one of the first and second aspiration aperture perimeters. 16.The electrosurgical wand of claim 14 wherein the first aspirationaperture extends a first distance beyond the first medial edge surfaceportion and the second aspiration aperture extends a second distancebeyond the second medial edge surface portion of the active electrodeand wherein the first distance is smaller than the second distance. 17.The electrosurgical wand of claim 14 wherein the first medial edgesurface portion of the active electrode has at least one internal cuspwith a first depth and the second medial edge surface portion of theactive electrode has at least one internal cusp with a second depth andwherein the first cusp depth is significantly smaller than the secondcusp depth.
 18. The electrosurgical wand of claim 13 wherein theaspiration cavity is characterized by an elongate funnel shape.
 19. Anelectrosurgical wand for treating tissue at a target site within or on apatient's body comprising: an elongate shaft defining a handle end and adistal end portion, the distal end portion comprising an activeelectrode, an insulative spacer body and a return electrode, wherein theactive electrode is disposed on a distal surface of the insulativespacer body and is spaced away from the return electrode; wherein theactive electrode defines a peripheral edge surface defining distal andproximal edge surfaces; wherein the insulative spacer body defines anaspiration cavity fluidly connected with an aspiration lumen andconfigured to aspirate fluid and plasma by-products therethrough, theaspiration cavity terminating on the distal surface of the spacer bodywith at least one cavity aperture, and wherein the active electrodecovers a portion of the cavity aperture so as to define at least oneaspiration aperture, the at least one aspiration aperture having aperimeter lying on a plane defined by the spacer body distal surface anddefined by the active electrode peripheral edge surface and a perimeterof the cavity aperture.
 20. The electrosurgical wand for treating tissueof claim 19 wherein the distal edge surface further comprises at leastone internal cusp and wherein the aspiration aperture perimeter isfurther defined by the distal edge surface and the at least one internalcusp.
 21. The electrosurgical wand for treating tissue of claim 19wherein the proximal edge surface further comprises at least oneinternal cusp and wherein the aspiration aperture perimeter is furtherdefined by the proximal edge surface and the at least one internal cusp.22. The electrosurgical wand for treating tissue of claim 19 wherein theaspiration aperture perimeter is further defined by a portion of theactive electrode peripheral edge surface that is shaped with an edgesurface geometry that elongates a perimeter of the peripheral edgesurface, configured to enhance vapor layer formation along theperipheral edge.